Synthesis of compound tones by vacuum-tube oscillators



March 24,1925. 1,530,498 B. W. KENDALL SYNTHESIS OF COMPOUND TONES BY VACUUM TUBE OSCILLATORS Filed NO). 20, 1917 /n VPHIOI: Bur/on M4 Kendall.

by My Patented Mar. 24, 1925;

UNITED STATES PATENT OFF/ICE.

BURTON W. KENDALL, OF YORK, N. Y., ASSIGNOR T WESTERN ELECTRIC COM- PANY, moonromrnn, on NEW YORK,

N. Y., A CORPORATION OF NEW -YORK.

SYNTHESIS OF COMPOUND TONES BY VACUUM IUBE OSCILLATORS.

Application filed November 20, 1917. Serial No. 202,938.

T 0 all whom it mag concern Be it known .that I, BURTON W. KENDALL, a citizen of the United States, residing at New York, in the county of New York and State of New York, have invented certain new and useful Improvements in Syntheses of Compound Tones by Vacuum-Tube Oscillators, of which the following is a full, clear, concise, and exact description. w

This invention relates to vacuum tube oscillators, and more particularly towhat are known as harmonic generators and to means for controlling the number and proportion of harmonics in the output of such generators. The invention may have various applications in arts where it is desired to produce a periodically varying current having certain definite numbers and proportions of harmonics or a tone having certain definite numbers and proportions of harmonics. Such tones are used, for example, in music. As the production of such a tone is preceded by the production. of the current in a suitale circuit, whichcurrent produces the tone by, acting through a suitable translating device, this specification will deal more specifically with'the production of tones, it-being understood that the generic aspect of the. invention contemplates production of the currents as aforesaid, either for the production of tones or for other purposes.

It is well known that a musical note, such as produced by the human voice or instru-' ments, consists of vibrations of some fundamental frequency, which we may denote by the" symbol F, combined with one or more of a series of overtones or harmonics of frequency 2F, 3F, 4F nF. The musical quality or timbre of the note depends on-the number and relative intensity of these harmonic components, the note of some instruments containing chiefly odd harmonics and of others even harmonics, While others contain both oddfand' even members of the series. In general, however, the higher members of the series are of small intensity or wholly lacking. v

.Itis known how to design and adjust a thermionic oscillation generator so as to pro 50 duce in the output circuit thereof, an oscillation of a fundamental frequency combined with a number of the harmonics thereof, the latter being present in appreciable amounts. The present invention consists, primarily, in

a means for and method of regulating the number of these harmonics and their relative intensities with respect to each other and the fundamental.

This is accomplished by the means shown in the accompanying drawings, wherein Fig. 1 represents diagrammatically a harmonic generator with the novel harmonic regulating means associated therewith; Figs. 2 and 3 represent two modified forms of harmonic regulating means for use with a harmonic generator as in Fig. 1, the line XX indicating the corresponding points of junction at XX in Fig. 1; and Fig. 4 represents a series of groups of such anti-resonant circuits asare found in Fig. 1.

Numeral 5 indicates an evacuated-vessel or tube of the audion type, which, with its connections, functions as harmonic oscillation generator H, while A, A represent similar vessels functioning as amplifiers. The tube 5 has its plate circuit arranged to feedback to the grid circuit through the coupled coils 9 of the plate circuit and 8 of the grid circuit. The path for the directcurrent in the plate circuit is through the coil 11 of high inductance, resistance 12 and the plate battery 7. The direct current flowing there through is practically constant andindependent of the frequency of oscillation. The.

tuning condenser 10 is shunted around coil 9 and, by adjusting it, andusing proper values of inductances '8 and 9 the oscillation frequency may be made any desired practical value. The oscillating currents do not passthroughthe coil 11 owing to its high.

inductance and the resistance 12, but pass principally through the path containing the condenser 13 and inductance coil '14. The

condenser 13 is of large capacity so that the impedance of this path is largely due to the coil 14, the function of the condenser bemg only to prevent passage of direct current.

in the same order of intensity. The tube 6 and its associated circuits constitute the amplifier A. The direct current output of amplifier A passes through resistance 16, induction coil 15 and plate circuit battery 17, while the circuit for the amplified alternating current passes through a large condenser 21 and a series of loop-resonant circuits 18, more usually known as anti-resonant circuits, each of which contains an adjustable condenser 19, adjustable inductance 20 and adjustable resistance 22. Each anti-resonant circuit may be short-circuited by a corresponding switch S.

Suppose the fundamental frequency of the oscillator H to be F and the harmonics 2F, 3F and 4F. The anti-resonant circuits 18 are made to be respectively loop-resonant or anti-resonant at frequencies F, 2F, etc., one circuit being present for every harmonic desired in the output. Suppose resistances 22 are adjusted to zero and switches S are open. Each circuit 18. will present a high mpedance to the harmonic'component of its own frequency and small impedance to other frequency components. This will result in all the components being impressed upon the grid-filament circuit of the amplifier A, as each anti-resonant circuit will furnish a source of voltage of its own particular frequency. This input is amplified and, by means of transformer 24, of which the primary is in output circuit 23 of tube 26, is impressed upon a suitable translating device as, for example, a receiver 25. The receiver 25 is intended to typify any suitable device or devices for translating electric energy into sound wave energy, such as an electrormagnetic or an electro-static receiver. If some frequencies preponderate, their proportionate intensity may be lessened as, for example, by adjusting resistances 22 and thereby varying the impedance of circuits 18. In case it is desired to elim-,

inate any frequency, the anti-resonant circuit corresponding thereto may be shortcircuited by its corresponding switch S.

For eflicient operation, the generator H should be overloaded, that is, the voltage variation of the input should be sufiiciently great so that the current variation of the output will cover a considerable range of the characteristic, extending upon curved portions thereof, thereby increasing the distortion, which, in general, increases the amplitudes of the harmonic components. In general, the oscillator will as a result of its inherent nature assume this operating condition. The amplifier A, on the other hand, should be only slightly loaded so that it. will produce substantially no harmonic-s. .[n Fig. 2 the anti-resonant circuits of frequencies F, 2F, 3F, 4F, are coupled to corresponding circuits, each containing an adjustable condenser 28, a resistance 29 and a coil 30, the latter being the means of coupling. The resistances 29' and the switches S serve similar functions to those in Fig. 1. The parts 23, 24, 25 and 26 are the same as in Fig. 1. In Fig. 3 the circuits 27 have resistances 31 connected across the condenser terminals. By adjusting these resistances both the functions of resistances 22 or 29 and switches S may be performed. The remaining elements correspond to Fig. 1.

In Fig. 4: the circuits 18 are tuned to be anti-resonant at the respective frequencies F, 2F, 3F and 4F, the circuits 32 are tuned to be anti-resonant at another series offrequencies F 2F,, 3F and tF An indefinite number of such series may be used, circuits 33 representing the last which are anti-resonant at frequencies F and the harmonies thereof. Then 'if frequency F corresponds to note C of the musical scale, F to C#, F to D, etc., it is possible'to secure in receiver 25 any desired note of the chromatic scale of-any desired quality. Switches S would normally be closed. Then suppose it be desired to produce the note C with its first harmonic. By adjusting condenser 10 so as to cause the fundamental oscillations to be of the frequency F and simultaneously opening switches S, which shunt circuits 18 of frequnecy F and 2F, the desired tone will be produced. In a similar manner any other fundamental note with any desired harmonic components may be caused to sound inreceiver 25.

In lieu of the compound series of antiresonant circuits in Fig. 4, the capacity, inductance and resistance of a single series, such as in Fig. 1, may be adjusted to be anti-resonant at one time to the note C and its harmonics, at another time to the note C# and its harmonics, etc. It is not essential that the same harmonic generator H be used for all notes, as one may be used for one note, another for another, and so on. The oscillations of several such tubes may be impressed at one timeacross the series of anti-resonant circuits, thus producing any desired combination of fundamental tones and their harmonics, or the outputs of sev eral amplifiers A, each connected to a different series of anti-resonant circuits and harmonic generator may be impressed upon a receiving instrument 25. In such manner any combination of tones may be pro duced. The anti-resonant circuits are not limited to a series of F, 2F, 3F and 41*, but may be extended to 91F where a represents any desired integer. All electrical element-s used, such as condensers, inductanees, resistances, couplings and battery voltages are, for convenience, made adjustable, unless it would be obvious that no adjustment would be useful. If a certain tone and its harmonics be represented by frequencies F, 2F, 3F, 4F, 5F, 6F, etc., it will be noted .that by eliminating the fundamental tone F and its odd harmonics, 3F, 5F, etc., there will be remaining the tone 2F and its harmonics 4F, 6F, etc. This would serve as a convenient method of securing tones of higher octaves with less multiplicity of apparatus. The harmonic generator and the parts to the left of the line XX in Fig. 1 are not in themselves new and no novelty is claimed therefor except in combination with other parts as her inafter indicated. The generator typifies any suitable means for producing currents of suitable frequencies having harmonic components in suitable amounts.

The parts, combinations and methods inherent in the invention which are believed to be novel are defined in the appended claims.

What is claimed is:

, 1. The method of producing a desired complex electric wave which comprises continuously generating a voltage wave including a plurality .of different frequency components of invariable amplitudes simultaneously produced, impressing said voltage wave upon an impedance path having large impedance to components which are to be of large amplitude in the wave to be produced and having relatively small impedance to components which are to be of small amplitude in or absent from the Wave to be produced, thereby selecting desired components and regulating their amplitude and utilizing the difference of potential across said pathfor setting up the desired Wave.

2. The method of producing a desired electric wave which comprises maintaining a.voltage containing all of the components of the desired wave and selecting therefrom appropriate proportions of the particular components necessary to produce the desired the differences of potential across said circuits as a source of potential for causing the desired wave.

4. The method of producing a desired form of wave of alternating current which consists in passing a given compound wave of current through a system of circuits, ad-

justing each' of said circuits to a desired Value of impedance to a certain frequency component of said given wave, amplifying the sum of the differences of alternating potential across said circuits, and impress: ing the amplified summation voltage upon a conductor.

5. The method of producing an alternating voltage having definite frequency components in definite proportions which comprises producing a sustained voltage wave having a plurality of different frequency components of invariable amplitudes simultaneously produced and impressing the produced wave upon a conductor whose impedances to the different components are relatively proportioned to produce a difference of potential thereacross having the definite components in the definite proportions which are desired.

6. Means consisting of anumber of circuits arranged in series, one of which is substantially anti-resonant at one frequency of current applied thereto and each of the others substantially anti-resonant at a multiple frequency thereof, and a device connected to the terminals of said series for utilizing the voltage thereacross.

7. Means according to claim 6 in combination with a series of switches, each switch when closed forming a shunt around one of said circuits. e

8. The combination of claim 7 inwhich the device connected to the terminals of the series of circuits comprises an amplifier, the extreme ends of said series being connected respectively to two input terminals of said amplifier.

9.A system comprising a number of circuits arranged in series, one of which is substantially anti-resonant at one frequency of current applied thereto and each of the others substantially anti-resonant at a mattiple frequency thereof, a one-way energy transferring device connected across the terminals of said series and an instrument associated with said device for producing sound waves from electrical waves.

10. The combination of a series of antiresonant circuits, one of which is antiresonant at a certain frequency and anotherat a multiple of said frequency, a source of electroinotive force, means for impressing said force across the terminals of said series, an amplifier, means for impressing the potential difference across a desired one or more of said circuits upon said amplifier.

11. Means for producing a desired compound recurrent electrical current wave containing given components in desired proportions including means for generating a current wave containing said components in other proportions, and means acted on by the energy of said generated current wave for regulating the proportions of the several components thereof to produce another current wave containing said components in said desired proportions.

12. The combination of a series of antiresonant circuits, one of which is antiresonant at a certain frequency and another at a multiple of said frequency, a source of electro-lnotive force, means for impressing said force across the terminals of said series, a translating device. and means for-impressing the potential difference across a selected number of said circuits simultaneously upon said translating device.

13. A source of compound electromotive force each of whose components consist of a fundamental and harmonics, means for simultaneously producing another electro motive force having selected components of said first mentioned electro-motive force,

and means for producing sound waves in accordance with the components of said second electromotive force.

14. A source for simultaneously producing an electromotive' force wave having a large number of different frequency components of predetermined amplitudes, means energizing said source to cause said source to continuously produce all of said components, means for simultaneously producing another sustained electromotive force comprising means for selecting desired components of said first mentioned electromet-ive force and varying their amplitudes to produce components having intensities of circuits, each-group consisting of a series of circuits, the first of said series of circuits containing members respectively anti-resonant at a frequency and harmonics thereof, others of said series of circuits containing members respectively anti-resonant at a second frequency and harmonics thereof, said frequencies being related to each other as the vibration frequencies of two selected tones of any-musical scale.

17 In combination, a harmonic "enerator, means associated therewith for causing said generatorto generate a plurality of fundamental frequencies, and means to produce from the various generated waves a combined wave having a fundamental frequency equal to one of said fundamental frequencies and selected proportions of harmonics thereof. I

18.111 combination, a harmonic generator, means associated therewith for causing said generator to generate a plurality of fundamental frequencies, and means to produce from the various generated Waves a complex note having a fundamental frequency equal to one of said'fumlamental frequencies and selected proportions of oer-- tain selected harmonics thereof.

19. In combination, a harmonic electrical generator, means to cause said generator to successive y generate a plurality of fundamental frequencies and their respective harmonies, means to produce therefrom currents lacking a part of said harmonic frequencies, and means to translate the electrical energy of the said currents into sound waves. v

20, An electrical system comprising electron discharge means, input terminals and an output circuit for said means, means comprising a plurality of tuned circuits each including an intensity regulating means for supplying a plurality of sets of audio frequency waves of selected intensity to said input terminals and a receiving device operatively. related to said output cir- I cuit responsive to effects produced by said waves, whereby a compound tone of regulable pitch and timbre may be produced.

21. An electrical circuit comprising electron discharge means having a plurality of input terminals and an output circuit, means comprising a plurality of tuned circuits each including an intensity regulating means for simultaneously supplying a plurality of sets of audio frequency waves of selected intensity to said input terminals, and a receiving device electrically connected to said output circuit so as to be responsive to the effect produced in said circuit by said sets of supplied waves, whereby a compound toneof regulable pitch and timbre may be produced.

22. A system comp-rising means-for supplying a plurality of electromotive forces each including a fundamental and one or more selected harmonics thereof, means for regulatingthe intensity of the-fundamental.

and selected harmonics of said electromotive forces, means for establishing a space current, and means for varying said current in accordance with the resultant electromotive forces, whereby a compound wave having regulable properties may be produced.

23. A system comprising means for continuously producing a plurality of harmonic elcctromotive forces, a space discharge re-' peater, a receiver associated with said repeater and 1 cans for selectively applying predetermine tromotive forces to. said repeater whereby a tone of any'pitch and timbre may be produced in said receiver,

24. A system comprising an] input conductor, a plurality of loop circuits serially connected there across, each loop circuit be ing' tuned to a different frequency and a translating device connected across 'a plurality of said circuits.

values of each of said elec- 25. A system comprising an input conductor, a series arrangement of loop circuits connected there across, each said circuit includin a eapacit element and an inductance e ement, a t ermionic repeater, an input circuit forsaid repeater, said input circuit being connected across a plurality of said 100 circuits.

nant at a certain frequency andothers at a e combination of a series of anti-- resonant clrcuits one of winch 1S anti-resomultiple of frequenoy, a source of electric waves, means for-impressing said waves across the terminals of said series, an amplifier, and means for impressing the potential difference across a desired one or more of said'cireuits upon said amplifier.

In witness whereof, I hereunto subscribe 11ny7name this 15th day of November A. D.,

BURTON w. KENDALL. 

